Scientists calculated the risk for young children who inhale cigarette smoke in the home can double compared with non-smoking homes, and increases for the under-fives.

The researchers concluded that exposure to second-hand smoke results in more than 600 additional children being affected by meningococcal disease - which causes the most dangerous form of meningitis - in Britain each year.

"We estimate that an extra 630 cases of childhood invasive meningococcal disease every year are directly attributable to second-hand smoke in the UK alone," said Dr Rachael Murray, who led the study.

"While we can't be sure exactly how tobacco smoke affects these children, our findings highlight consistent evidence of the further harms of smoking around children and during pregnancy," she said, adding that 'parents and family members should be encouraged to not smoke around children'.